OMAP: iommu: fix wrong argument in flush_cache_vmap()

The second argument should be the end address, not the
length. Actually there will not be any effect on the behavior of this
driver since flush_cache_vmap() calls flush_cache_all() in the end.

Signed-off-by: Hiroshi DOYU <Hiroshi.DOYU@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>